Machine for hobbing the teeth of gear wheels



K. L. OLIVER 2,926,569.

MACHINE FOR HOBBING THE TEETH OF GEAR WHEELS March 1, 1960 7 Sheets-Sheet 1 Filed Feb. 18, 1953 BY 7 W ATTORNEYS March 1960 MACHINE FOR HOBBING THE TEETH OF GEAR WHEELS 7 Shee'Es-Sheet 2 Filed Feb. 18, 1953 ATTORNEYS Marh 1, 1960 K. L. OLIVER 2,926,569 MACHINE FOR' nossmc THE TEETH OF GEAR WHEELS Filed Feb. 1a, 1955 v 7 Sheets-Sheet 3 ATTORNEYS March 1 1 OLIVER MACHINE FOR HOBBING THE TEETH 0F GEAR'WHEELS Filed Feb. 18, 1953 INVENTOR ATTORNEYS K. L. OLIVER March 1, 1960 MACHINE FOR HOBBING THE TEETH OF GEAR WHEELS Filed Feb. 18. 1953 7 Sheets-Sheet 5 )INVENTOR March 1, 1960 K. L. OLIVER 2,926,569

, MACHINE FOR HOBBING THE TEETH OF GEAR WHEELS j Fil ed Feb. 18. 1953 '7 Sheets-Sheet 6 g: FIG. IO.

l I I v INVENTOR ATTORNEYS K. L. OLIVER 2,926,569

MACHINE FOR HOBBING THE TEETH 0F GEAR WHEELS March 1, 1960 7 Sheets-Sheet 7 Filed Feb. 18, E953 FIG. I I.

T VERSE CCORD THE INVENTION WORM ANGLE OF HOB.

mv ENTo z 1 v s ATTORNEYS United Stt MACHINE FOR HOBBING THE TEETH OF GEAR WHEELS Application February is, 1953, Serial No. 337,623

3- Claims. c1. 90-4 The invention relates to the hobbing of the teeth of helical and spur gears, particularly helical gears, and it has for its object to provide an improved method of and machine for the purpose which will not only enable the rate of production to be speeded up but which, by reason of the constructional simplicity of the machine, will enable gears of very accurate tooth form to be produced.

The method of hobbing gear teeth according to the invention is characterised in that a hob and a gear blank, rotated in appropriately timed relation, are so relatively positioned and are given such relative traverse or feed that the hob teeth, after having been fed radially the desired distance towards the blank, travel in a direction parallel to the helix of the teeth to be cut.

In a hobbing machine as hitherto constructed, it has been necessary, for a reason well known to those skilled in the art,'to provide, for the cutting of helical gears, means for enabling what is known as a compensating rotation to be given either to the hob or to the blank.

It is also usual to provide means to shift the hob axially during cutting or between cutting operations, so that wear will be distributed over a predetermined length of the hob. 1

An advantage afforded by hobbing according to the improved method above referred to is that no provision is necessary for giving compensating rotation to the hob or to the blank.

A further advantage is that the distance required to be traversed by the hob is reduced as compared. with that necessary in the usual conventional hobbing machines, thus enabling production to be speeded up.

A machine for carrying out the invention may comprise a work carrier or cradle capable of being adjusted angularly about a horizontal. axis to cause the axis of a blank carried thereby ,to occupy any desired angle; a cutter slide capable of being traversed vertically, conveniently by hydraulic. means; means to permit a hob carried by the cutter slide to be adjusted to a position in which its axis occupies. a predetermined angle relative to the centre distance between the hob and the blank;

and means for rotating the hob and the blank in predetermined timed relation.

The axis of the hob is so adjusted angularly, in relation to the plane in which it is moved by the traversing of the cutter slide, that its teeth travel in a vertical plane, that is to say its axis is caused to occupy, in relation to the horizontal, an angle equal to the worm angle of the hob.

The axis of the blank is caused to occupy, in relation to the axis of the hob, such an angular position that the hob teeth, as the hob is fed or traversed vertically through the blank, will mill out tooth gaps in the blank at the desired helix angle.

The traversing of the hob through the blank and its return to initial position may conveniently be effected by hydraulic means, and appropriate control means may be provided whereby when the hob has moved clear of the blank, that is to say when it has finished cutting the atent though of course any other suitable form of clamping means may be employed.

I By reason of the swivelling of the blank to the helix angle of the teeth to be cut and the traversing or feeding of the hob directly down the helix, no compensating rotation of the hob or of the blank is necessary. This means that such gearing as spiralling change gears and/or differential mechanism can be dispensed with andthis, by reducing backlash and so forth, makes for the production of accurately finished tooth surfaces.

When a helical gear is being cut the hob automatically traverses across the centre line of the blank, the extent of such traverse depending upon the angle of inclination of the blank, that is to say upon the helix angle of the teeth being cut and upon the face width of the blank. Manually operable means may, if desired, be provided to enable the hob to be periodically moved axially so that wear may be distributed along its whole length.

Since the hob is traversed vertically across the face of the blank, the actual length of traverse as compared with that required for conventional hobbing is reduced by an amount dependent upon the helix angle of the teeth being cut. This obviously makes for increased production.

Such being a brief outline of the invention a practical embodiment of the same will be described with the aid of the accompanying drawings in which:

Fig. 1 is a front view and Fig. 2 a plan view of the main parts of a gear hobbing machine, according to the invention;

7 Fig. 3 is a side view of the machine looking in the direction of the arrow 3 in Fig. 2;

Fig. 4 is a rear view of the machine;

Fig. 5 is a diagrammatic view of the driving arrangement of the machine;

Fig. 6 is a detailed view showing the adjustable mounting for the hob;

Fig. 7 is a detailed'view illustrating diagrammatically the drive for the work spindle;

Fig. 8 is a sectional elevation on an enlarged scale of the means for clamping the work-piece;

Fig. 9 is an elevation also on an enlarged scale of the means for moving the slide carrying the hob towards and away from the'workpiece and for moving it vertically;

Fig. 10 is a diagram illustrating the hydraulic system employed to control the operation of the machine; and

Fig. 11 is a diagram illustrating the reduction effected according to the invention in the required traverse of the hob as compared with that required in a hobbing machine of the hitherto conventional type.

Referring to the drawings, 1 represents a suitable bed or frame having a vertical portion 1a in an opening in which is mounted to rotate about a horizontal axis a work carrier or cradle 2 in bearings in which there is rotatably mounted a workspindle 3, having secured to its upper end an adapter 3a. Also on the frame 1 are horizontal guide 1b on which is, slidable towards and away from the work spindle 3, a column 4 having vertical guides 5 on which is moveable a cutter slide 6 carrying ahob 7.

The work carrier or cradle 2 is adjustable angularly by means of a hand wheel 8, worm 9, worm wheel 10, shaft 11, and a worm 12 which engages a toothed segment 13 on the carrier. Clamps l4 enable the carrier to be secured in the desired angular position. An opening 15 in the front face of the carrier gives access to a Work piece 16 clamped to the work spindle 3 and also enables access to be had to the hob 7.

An electric motor 17 mounted on the bed 1 drives by means of pulleys 18 and 19 and belts 20 a shaft 21 which, by a pair of pick-off or change gears 22 and 23 drives a shaft 24. By means of bevel gears 25 and 26 drive is transmitted from shaft 24 to a main drive shaft 27 from which both work spindle 3 and bob 7 are driven.

The shaft 27 is connected through change gear 28 to a work-drive shaft 29 connected by a pair of mitre gears 30 and 31 to an angularly movable sliding shaft 32. This shaft 32 is by another pair of mitre gears 33 and 34 connected to a shaft 35 carrying a worm 36 which meshes with a worm wheel 37 fast with the work spindle 3. As the carrier 2 is adjusted angularly a suitable connection between the shafts 35 and 32 causes the gears 34 and 33 to remain in mesh and the shaft 32 to slide through the gear 31 thus maintaining the drive connection between the said gear 31 and the gear 30. This action will be understood from the diagram Fig. 7. In this diagram the work spindle 3 is shown in a central vertical position in which the sliding shaft 32 occupies the position shown in full lines. The two extreme positions, corresponding to the movement of the carrier and thus of the axis of the work spindle through an arc of 45 to either side of the vertical, are shown in broken lines.

The shaft 27 is also connected by bevels 38, 3940 a vertical splined shaft 40 which, through a clutch 41, can be connected to either of two bevel gears 42, 43 slidably mounted on the shaft 40 and which both mesh with a bevel gear 44 fixed on a shaft 45. This shaft 45 is connected by gears 46 and 47 to a shaft 48 carrying a worm 49 which meshes with a worm wheel 50 on-the spindle 51 carrying the bob 7. By appropriate operation of the clutch 41 the direction of rotation of the hob can thus be reversed.

The hob spindle 51 together with the gear 50, worm 49, shaft 48 and gear 47 are carried by a bracket 6a see Fig. 6, on the cutter slide 6 so that the axis of the hob can be so adjusted angularly that its teeth will, as the cutter slide is moved vertically, travel in a direction parallel to the helix of the teeth to be cut in the blank. This will be understood from the diagram Fig. 11.

The weight of the cutter slide 6 and of the parts carried thereby that is to say the hob 7, shaftSl, worm wheel 50, worm 49, shaft 48, gears 47 and 46, shaft 45 and bevel gear 44, is shown as being balanced by a weight 52 to which it is connected by a flexible connection 53 passing over guide pulleys 54.

The means employed for clamping a work blank 16 to the work spindle 3 are shown in Fig. 8. The spindle 3 is hollow and has disposed axially in its lower part a rod 56 with a nut 57 fixed on its extremity. Between the nut 57 and a shoulder 58 constituted within the hollow spindle there is confined under suitable compression a coil spring 59. To the upper end of the rod 56 there is secured a clamping member 60 the head 61 of which is adapted to press, through a C washer 62 upon the upper face of the work piece and clamp it against the upper end of the adapter on the hollow work spindle. Below the rod 56 there is constituted a hydraulic cylinder 63 containing a piston 64 a central upward projection 65 on which is adapted to abut against the lower extremity of the rod 56. Above and suitably spaced from the upper end of the work spindle there is provided on the carrier 2 a hydraulic cylinder 66, see Fig. 10, the piston or plunger 67 of which carries a freely rotatable centre 68. To enable the blank 16 to be inserted into the mmchine the centre 68 is raised to an appropriate height and the clamping member 60 is also raised by admission below the piston 64 of liquid at a pressure suflicient to compress the Spring 59. The blank having been placed in position to rest upon the upper end of the adapter fast with the work spindle and the C washer 62 having been inserted between the upper face of the blank and the head 61 of the clamping member 60, the pressure beneath piston 64 is released thus permitting the spring 59 to act to draw the clamping member 60 downwardly and clamp the blank tightly to the work spindle. The centre 68 is then lowered to engage with its tip in a recess in the upper end of the head 61 of the clamping member 60. To release the finished work piece pressure fluid is readmitted below the piston 64 to raise the clamping member 60 sufliciently to permit removal of the C washer 62.

Having thus described the construction of the main relevant parts of the machine its operation will now be described. This will be done with the aid of the diagram Fig. 10 which illustrates the hydraulic system employed to control in their proper sequence the operation of the various movable elements constituting the improved machine.

A pump 69, driven by a suitable motor not shown, draws liquid through a filter 70 and supplies it under suitable pressure to a solenoid-operated fourway valve 71. This valve is adapted, on being energised, to supply pressure liquid below the piston 64 and thus to raise the clamping member 60 to permit the insertion of a blank to be cut. De-energising of the valve 71 then releases pressure from below the piston 64 and permits spring 59 to effect clamping of the blank to the work spindle. The valve 71 also passes pressure fluid to a double-solenoid fourway valve 72. When the solenoid of the valve 71 has been de-energised, the valve 72 is operated to direct pressure fluid to the upper end of the cylinder 66 thus causing the rotatable centre 68 to be fed down into the clamping member 60 to steady the work spindle. A manually operable cut-out valve 710 is provided between the valve 71, and the clamp release cylinder 63 to enable the blank clamping means to be put out of action if desired.

The pump 69 also supplies pressure liquid through a pressure relief valve 73 and a non-return valve 74 to a double-solenoid fourway valve 75.

The blank having been clamped to the work spindle as above described, the valve 75 is operated to direct pressure fluid to a sequence valve 76 through which it passes without obstruction and thence by way of a fluid control valve 77 to one end of a hydraulic cylinder 78 carried by the column 4, to cause the said column to be moved towards the work spindle a suflicient distance to feed the hob 7 the required depth into the blank, the extent of such inward feeding movement being determined by contact of the column with a suitable stop. In addition to the column 4 being guided at its lower end, it has at its upper end a projection 4a which is guided in a groove in a bracket 4b carried by the vertical portion In of the base 1. Liquid expelled from cylinder 78 by inward feeding movement of the column 4 passes by way of a counter balance and check valve 79, a sequence valve 80, and ports in the valve 75 back to the sump. When the inward feeding movement of the column 4 is arrested, pressure builds up in the sequence valve 76 and causes the pressure to be directed to a sequence valve 81, through which it passes straight to the hydraulic cylinder 82 to cause clamping bolts 83 to be operated to clamp the column 4 in position. When the clamping movement of the bolts 83 is arrested pressure builds up in the valve 81 and causes pressure liquid to be directed to a double-solenoid fourway valve 84. This valve operates to pass liquid through a counter-balance and check valve 85, a flow-control valve 86 and a flow-diverting valve 87 to' the upper end of a hydraulic cylinder 88 containing a fixed piston 89. The valve 87 is operable manually to cause the valve 84 to pass pressure fluid either to the upper end of cylinder 88 if cutting is to take place during upward movement of the cutter slide or to the lower end of the said cylinder if cutting is to take place on the down ward movement of the slide.

85a is a counter-balance and check valve similar to the valve 85 and co-operates with it in balancing the movement or" the cutter slide.

The cylinder 83 is carried by the cutter slide 6, so that the admission of pressure fluid to its upper end causes the cutter slide to be fed upwardly at a speed determined by the setting of the flow control valve 86. When the cutter slide reaches its upward determined limit of movement it operates a trip switch and its movement is arrested.

The operation of the trip switch causes the valve 75 to be changed over and the valves 76'and 81 opened up to the sump. This releases the pressure in the cylinders 82 and permits the springs 90 behind the pistons 91 to move the clamping bolts 83 in a direction to release the column 4. Simultaneously pressure liquid is directed to the valve 80 causing pressure liquid to be now directed through valve 79 to the cylinder 78 to move the column 4 in quick motion in a direction to carry the hob clear of the work piece until the movement of the column is arrested by its contacting a suitably positioned stop incorporating a limit switch which functions to operate the valve 72 to'feed the centre 68 upwardly clear of the head 61 of the clamping member 60, and to operate the valve 84 to cause the cutter slide 6 to feed rapidly downwardly back to its starting position, on arrival at which it contacts a switch and switches oif the main motor thus completing a work cycle.

Whilst the operation of the valves 71, 72, 75 and 84 in the correct sequence and at the appropriate times is preferably controlled automatically, hand-operable control means will also be provided for use when setting up the machine. A pilot valve is provided at 95 to enable the operation of the clamping bolts 83 to be cut out when setting up the machine.

The principal advantage afforded by the improved method of hobbing and by the machine for carrying out such method will be apparent from an examination of the diagram shown in Fig. 11. This represents a work blank 16 in which teeth are to be cut having a helix angle of 30. If hobbing were carried out according to the conventional method the hob would require to have a traverse the length of which is indicated by the distance 92. By the method according to the invention in which the blank and the hob occupy ,such relative positions and are given such relative traverse or feed that the hob teeth travel in a direction parallel to the helix of the teeth to be cut in the blank, the amount of traverse necessary to be given to the hob after it has been fed radially into the blank to the depth of tooth to be cut is only that indicated by the distance 93.

It will be understood that the longitudinal centre line 94 of the blank, at the mid point in the depth of the blank, passes through the centre 95 about which the blank is adjustable angularly by partial rotation of the carrier 2, and at that point intersects the vertical line 96 along which in its cutting movement the hob is traversed upwardly from the lower to the upward position shown in Fig. 11.

In addition to the foregoing advantage the construction of the machine is considerably simplified by theabsence of any necessity to make provision either for giving compensating rotation to the hob or to the blank. Whilst the direction of traverse given to the hob relative to the blank causes wear to be distributed over a cer- 6 tain length of the hob dependent upon its worm angle manually operable means may be provided to enable the hob to be periodically moved axially so that wear may be distributed over its entire length.

Whilst the method of operation shown in the diagram Fig. l1 is preferred by reason of the reduction it affords in the. required distance of traverse of the hob, it is not arbitrary. The hob may commence its movement from a point below and clear of the blank, having been previously fed radially towards the axis of the blank to such a distance that in its upward movement it will take a cut of predetermined depth. The upward movement may be continued until the hob is clear of the blank, the hob being then withdrawn a short distance clear of the base of the tooth gap and returned to its starting position below the blank, where it is again fed radially before its next upward cutting movement.

It is to be noted that the work carrier for cradle 2 is annular in form (see Figures 1, 7), with the work spindle 3 located within it in a plane perpendicular to the axis of carrier 2, the carrier being rotatable Within the vertical portion 1a of bed 1 to adjust the angular disposition of work spindle 3. The purpose of the annular work carrier is to insure that the gear blank will be rigidly mounted during the hobbing operation while permitting easy and accurate angular adjustment of said blank relative to the hob.

Having thus described my invention, what I claim as new and desire to secure by Letters Patent is:

1. A machinefor hobbing the teeth of gear wheels, comprising a spindle adapted to carry a hob, and means for rotating said spindle; means for mounting a hob on said spindle; a work spindle and means for rotating it in predetermined relation with the rotation of the hob; means for varying the distance between the hob spindle and work spindle; an annular carrier for the work spindie, the axis of the said spindle being located within the carrier in a plane perpendicular to the axis thereof and the carrier being rotatable to adjust the angular disposition of the work spindle axisjmeans for clamping a gear blank on the work spindle; means for traversing the hob across the face of the blank; and means for adjusting the hob spindle to a position in which its axis occupies a predetermined angle relative to the direction in which the hob traverses the gear blank.

2. A machine as in claim 1 wherein said last-mentioned means is adapted to enable the angular position of the axis of the hob to be so adjusted that as the hob is trav ersed, its teeth travel in a direction parallel to the helix of the teeth to be cut in the blank.

3. A machine for hobbing the teeth of gear wheels comprising a bed; an annular work carrier located with its axis horizontal Within a vertical portion of the bed; means for rotating the work carrier about its axis; a work spindle journalled within the work carrier with its axis radial to the work carrier axis; means for clamping a gear blank on the work spindle; hydraulic means for moving a center into and out of engagement with the end of the work spindle which is adapted to carry the gear blank; hob slide support means guided on the bed for movement towards and away from the work spindle; hydraulic means for moving said column in said direction; vertical guides on said column, in a plane perpendicular to the work carrier axis; a hob slide movable on said guides; hydraulic means for moving the hob slide; a bracket carried by the hob slide and adjustable angularly about an axis perpendicular to the plane of said guides; a spindle journalled on said bracket with its axis in a plane perpendicular to the work carrier axis, and adapted to carry a hob; and means for rotating the hob spindle and work spindle in predetermined timed relation.

(References on following page) References Cited in the file of this patent UNITED STATES PATENTS 'Pfauter Jan. 2, 1900 Zimmermann June 6, 1939 Kruse Feb. 17, 1942 Carlsen Sept. 1, 1942 Schurr et a1 Apr. 13, 1943 Purvin Aug. 29, 1944 Davenport Apr. 24, 1945 Barnard et a1 Jan. 28, 1947 Ransome Oct. 12, 1948 Felin et a1 Mar. 1, 1949 8 Cotta Oct/4, 1949 Praeg Mar. 6, 1951 Miller July 24, 1951 Warner Aug. 14, 1951 Praeg et a1. Aug. 28, 1951 Staples July 20, 1954 FOREIGN PATENTS Australia Apr. 30, 1951 OTHER REFERENCES Gear Cutting Machinery, Flanders, 1909, pages'173- 

